Most smoke detectors include a body which defines a chamber with openings to the surrounding air within which any airborne smoke particles can be detected. The chamber forms a controlled environment for detection. The chamber can be arranged such that it is insulated from entry of ambient light, and that the openings prevent ingress of insects and larger dirt particles. So long as the openings are kept clear of dirt, such smoke detectors have proven to be extremely reliable and to require limited maintenance.
Chamberless smoke detectors are a recent development, and as their name suggests, they are designed to detect smoke without using a chamber in the air outside of the body of the detector. Chamberless smoke detectors have the aesthetic advantage of having a lower profile because they do not require the body to include a chamber. Chamberless smoke detectors include a faceplate and smoke particles are detected in a detection region in front of the faceplate. One of the challenges in designing a chamberless smoke detector is that the detection region is not a controlled environment, and objects and light can enter the detection region without hindrance, which can result in the raising of false alarms too frequently. For example, an insect could enter the detection zone and cause a false alarm to be triggered. Alternatively, an object carried by a person might inadvertently be moved through the detection zone and cause a false alarm to be triggered. It is necessary to ensure that false alarms are minimised in order to save unnecessary disruption from unnecessary evacuations and to minimise call-outs from fire services and maintenance technicians.
A known chamberless smoke detector is the Bosch FCP-500. That detector seeks to minimise false alarms by having two smoke detectors mounted on the body which have completely separate detection regions so that, if an insect or object passes in front of the detector, it will only be detected by one detector at a time.